Diamond abrasive grain and electroplated tool having the same

ABSTRACT

A coating method on diamond abrasive grains is used to form a conductive film on diamond abrasive grains. The conductive film has chemical composition gradient giving the diamond abrasive grain an outwardly increasing electrical conductibility as a function of film thickness. The subsequent electroplating layer can therefore more effectively embed the modified diamond abrasive grains, whilst the adhesion/bonding strength between substrate (work piece for electroplating) and the diamond abrasive grains is improved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to diamond abrasive grains. In particular,the present invention relates to diamond abrasive grains havingelectrical conductivity and electroplated tool having the same.

2. Description of Related Art

Diamond tools (i.e., abrasive tools) are widely used in semiconductormanufacturing industries, machining industries, aerospace industries andthe polishing industries. The applications including cutting, drilling,sawing, grinding, lapping and polishing. The diamond tools are usuallymanufactured by electroplating methods.

One specific process that uses the diamond tools is chemical mechanicalpolishing (CMP) and this process has become standard in thesemiconductor and integrated circuit industries for polishing thewafers. As well known, a CMP pad is used in a planarization of wafersand a CMP pad conditioner is a type of grinding tools for improvingperformance and life of the CMP pad. The CMP pad conditioner can beproduced by bonding the diamond abrasive particles, e.g., by brazing orelectroplating, onto a metal substrate. For improving the bondingstrength of the diamond abrasive particles and the substrate in theelectroplating method, the surface of the diamond abrasive particles maybe modified to be conductive. Thus, the electroplating layer may coverthe diamond abrasive particles so as to avoid the diamond pop-out duringapplication process.

Sapphire substrates are well-known materials in LED industry. One methodof marking sapphire substrates is utilizing a metal wire with diamondslurry to cut the ingot. However, the diamond slurry has a high priceand thus the manufacturing cost is high. On the other hand, the cuttingrate is slow. Now, a precision diamond wire saw (PWS) has been developedfor manufacturing the sapphire substrates. The PWS can be produced bybonding diamond abrasive particles, e.g., by electroplating, onto ametal wire. By using the PWS instead of traditional slurry cutting, thesapphire ingot cutting time can be reduced from days to hours.

In a traditional method of the electroplating, the un-modified diamondabrasive particles are mechanically bonded into the electroplatingmatrix. However, the diamond abrasive particles often cannot be firmlyfixed in the electroplating layer due to insufficient metal matrixcoverage and week mechanical supporting strength surrounding the diamondparticles. During application process, the diamond abrasive particlesmay easily pop-out from the metal matrix (i.e., the metal substrate orthe metal wire). The popped-out diamond abrasive particles may damagethe processing materials, i.e., wafer or glass. For increasing thebonding strength, the thicker electroplating layer is required to firmlyfix the diamond abrasive particles. However, when the diamond abrasiveparticles are covered by the thicker electroplating layer, it willresult-in less free-cutting ability.

Although the commercial coating for diamond particle, such as Ticoating-or Cr coating layers are widely used in the market, the metalcoating layer has high electrical conductivity so that the coateddiamond abrasive particles are easily stacked one another to formdiamond clusters or nodules when processed in electroplating bath.

SUMMARY OF THE INVENTION

One object of the instant disclosure is providing diamond abrasivegrains which have an electrical conductive layer with micro-conductivityon the respective surface. As the character of conductive layer, a fullcoverage and chemical boned metal layer can be plated on the surface ofthe diamond abrasive grains in electroplating process. Thus, the bondingstrength between the diamond abrasive grains and the substrate will beimproved.

Another object of the instant disclosure is providing diamond abrasivegrains which have a conductive layer thereon. The conductive layer hasan increasing electrical conductibility because the gradient of chemicalcomposition.

The instant disclosure provides diamond abrasive grains which have aconductive layer thereon. The conductive layer has micro-conductivityand the electrical conductibility of the conductive layer increasesoutwardly from the surface of the diamond abrasive grain.

The instant disclosure provides an electroplated abrasive tool includinga substrate (e.g., an abrasive surface of the abrasive tool) and aplurality of diamond abrasive grains. The diamond abrasive grains arefirmly disposed on the abrasive surface of the substrate by anelectroplated metal matrix. Each of the diamond abrasive grains includesa conductive layer on a surface of the diamond abrasive grain. Theconductive layer has an increasing electrical conductibility as afunction of the conductive layer thickness and the compositionalgradient.

Accordingly, the instant disclosure provides diamond abrasive grainswhich have an increasing electrical conductibility. The electricalconductibility of the diamond abrasive grains is increasing from thesurface of the diamond abrasive grain outwardly. Thus, the electroplatedmetal may cover the surface of each diamond abrasive grain entirely orpartially by controlling the gradient of conductive layer compositionand the bonding strength between the diamond abrasive grains and thesubstrate can be improved. Due to the increased bonding strength, thediamond abrasive grains may not pop-out easily from the-substrate of theelectroplated tool in sawing or polishing processes. Therefore, thesurface accuracy of the electroplated tool can be controlled in thesawing or grinding/polishing processes.

For further understanding of the present invention, drawing reference ismade as the following detail description illustrating the embodimentsand examples of the present invention. The description is forillustrative purpose only and is not intended to limit the scope of theclaims

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the diamond abrasive grains of the instant disclosure.

FIG. 2 shows the electroplated tool of the instant disclosure, whereineach diamond abrasive grain is partially covered by the electroplatedmetal matrix.

FIG. 3 shows the electroplated tool of the instant disclosure, whereineach diamond abrasive grain is entirely covered by the electroplatedmetal matrix.

FIG. 4 shows a relationship between the flow rate of C₂H₂ and theconductivity of the conductive layer of the instant disclosure.

FIG. 5 shows a PECVD method to deposit the conductive layer on thediamond abrasive grain of the instant disclosure.

FIG. 6 shows an AIP method to deposit the conductive layer on thediamond abrasive grain of the instant disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The instant disclosure provides a diamond abrasive grain having modifiedsurface. By modifying the surface of the diamond abrasive grain, thediamond abrasive grain has micro-conductivity so that the diamondabrasive grain can be firmly fixed on a surface of a substrate and anelectroplated layer can be controlled for diamond particle coveragepercentage. Thus, the bonding strength of the diamond abrasive grain onthe substrate can be improved and the electroplated tool can have longertool life and better grinding surface accuracy.

The instant disclosure provides a modifying method of the surface of thediamond abrasive grains, and the method includes the following steps:

Please refer to FIG. 1; step 1 is providing the diamond abrasive grains11. In the exemplary embodiment, the diamond abrasive grains 11 can benatural or synthetic (i.e., artificial) micro-sized/nano-sized diamondpowders, but not restricted thereby. Preferably, the average size of theexemplary diamond abrasive grains 11 is ranged from 1 um to- 600 um.

Step 2 is providing a coating method to coat and form a conductive layer12 on the surface of the diamond abrasive grains 11. The coatedconductive layer 12 has a metal content, a metal-carbide content or ametal-nitride content therein and the metal content, the metal-carbidecontent or the metal-nitride content have a gradient of chemicalcomposition so that the diamond abrasive grains 11 have a property ofmicro-conductivity. In detail, the electrical conductibility of theconductive layer 12 is configured as a function of the conductive layerthickness and the compositional gradient; preferably, the composition ofthe metal content, the metal-carbide content or the metal-nitridecontent is a gradient from the surface of the diamond abrasive grain 11outwardly. In an exemplary embodiment, a PECVD (plasma enhanced chemicalvapor deposition) process is applied in step 2 and the exemplary PECVDprocess is set forth in FIG. 5. As can be seen in FIG. 5, the diamondabrasive grains 11 are placed in a rotatable vacuum deposition chamber31. A pumping device 32 incorporating with a vacuum gauge 33 evacuatesthe vacuum deposition chamber 31 and maintains the gas flow and pressureof the supplied gases, such as acetylene (C₂H₂), inert gases.Furthermore, suitable saturated metal compounds are employed andintroduced into the vacuum deposition chamber 31. By using a generator34 for initializing plasma of the introduced gas mixture, the conductivelayer 12 is coated on the surface of the diamond abrasive grains 11 andthe conductive layer 12 has a metal content therein. Preferably, themetal content may include boron (B), tungsten (W) or transition metals,and the transition metals, for example, comprise titanium (Ti), chromium(Cr), vanadium (V), zirconium (Zr) and so on. Due to the energy gapprofile across the thickness of conductive layer 12, the conductivelayer 12 performs as a conductive shell on each diamond abrasive grain11. On the other hand, by varying the content composition of the metalcontent, an increasing electrical conductibility as a function of thethickness of the conductive layer 12 is achieved. For one example, thesaturated or unsaturated TiCl₄ is introduced into the PECVD process toform a titanium-containing conductive layer 12 and the Ti-carbidecontent or the Ti-nitride has an increasing compositional gradient fromthe surface of each diamond abrasive grain 11 outwardly. Thus, theelectric resistance of the conductive layer 12 is gradientally decreasedin the direction away from the surface of the diamond abrasive grain 11;in other words, the electrical conductibility is increased. According tothe experimental results, the electric resistance of the conductivelayer 12 is decreased and ranged from 80 mΩ-cm to 20 mΩ-cm. Therefore,the metal content of the present invention is not restricted thereby andit is required that the electric resistance of the conductive layer 12is decreased and ranged from 80 mΩ-cm to 20 mΩ-cm so that the issue ofthe diamond cluster stacked by the diamond abrasive grain 11 may beavoided in the electroplating process.

In another exemplary embodiment, an AIP (Arc ion plating) process isapplied in step 2 as illustrated in FIG. 6. A pumping device 43evacuates the chamber and maintains the gas flow and pressure of thesupplied gases, such as acetylene (C₂H₂), inert gases (such as Ar). Ametal target 44, such as Cr target is provided to generated arcdischarging plasma by applying current from power supply 41 and themetal target 44 is ionized and vaporized. On the other hand, a biaspower supply 42 is able to apply a negative pulse bias voltage to thediamond abrasive grains 11. According to the negative voltage isapplied, the bombardment treatment of the ionized metal can be performedand results in the deposition on the surface of the diamond abrasivegrains 1. By executing the deposition reaction by changing the flow rateof the acetylene (C₂H₂) decreased from 200 sccm to 40 sccm, the electricresistance of the conductive layer 12 is decreased and ranged from 80mΩ-cm to 20 mΩ-cm as shown in FIG. 4. Preferably, suitable gas flow ratemay be applied in the deposition process so as to obtain a lowconductivity area 12A (i.e., the inner portion proximate the surface ofthe diamond abrasive grain 11) of the conductive layer 12 having anelectric resistance ranged from 70 mΩ-cm to 100 mΩ-cm and a highconductivity area 12B (i.e., the outer portion away from the surface ofthe diamond abrasive grain 11) of the conductive layer 12 having anelectric resistance ranged from 5 mΩ-cm to 20 mΩ-cm.

While initializing the deposition process by introducing the higheracetylene (C₂H₂) flow rate, the metal content is a metal-carbidecontent, such as C—Cr compound having a chemical formula of Cr_(x)C_(y),for example, Cr₂₃C₆, Cr₇C₃, Cr₃C₂ and so on. By decreasing the flow rateof the acetylene (C₂H₂), the composition of the metal content, such asCr content in the conductive layer 12 may increase so that the electricresistance is decreased (i.e., the electric conductivity is increased).Similarly, the tungsten (W) content in the conductive layer 12 may beformed as W—C content in a suitable processing condition and thevanadium (V) content in the conductive layer 12 may be formed as V—Ccontent in a suitable processing condition. In other words, the metalcontent in the conductive layer 12 may be formed as metal-carbidecontent, such as C—Cr compound, C—W compound, C—V compound, C—B compoundand so on. The metal-carbide content of the conductive layer 12 has agradient of chemical composition increased from the surface of thediamond abrasive grain 11 outwardly so that the conductive layer 12 hasan increasing electric conductivity to improve the performance of theelectroplating. In an alternative embodiment, the metal content of theconductive layer 12 may be formed as metal-nitride content in a suitableprocessing condition.

The present coated diamond abrasive grains 11 can be mounted on asurface of a substrate 21 by an electrodeposition/electroplating method,such as a nickel (Ni) electroplating method. The substrate 21 may be awire, CMP pad conditioner or a grinding/polishing tool made of steel,stainless steel, aluminum alloy, titanium alloy or alloy steel. As shownin FIG. 2, the electroplated metal matrix (e.g., an electroplated layer)22 extends from the surface of the substrate 21 onto the diamondabrasive grains 11 along the conductive layer 12 due to themicro-conductivity of the conductive layer 12 of the diamond abrasivegrains 11. In the embodiment, the electroplated metal matrix 22 ispartially plated on the diamond abrasive grains 11. Because that thediamond abrasive grains 11 are grabbed by the electroplated metal matrix22 resulted from the electroplating process on the conductive layer 12,the diamond abrasive grains 11 are firmly and stably bonded on thesurface of the substrate 21 so as to form an electroplated tool. In thisembodiment, the partial surface of the diamond abrasive grains 11 isexposed from the electroplated metal matrix 22 so that the electroplatedtool provides better sawing or polishing performance.

Alternatively, for further bonding the diamond abrasive grains 11 on thesubstrate 21, the diamond abrasive grains 11 are entirely covered by theelectroplated metal matrix 22 by controlling the gradient of conductivelayer composition, as shown in FIG. 3.

The advantages of the instant disclosure are following:

1. Comparing with the traditional and un-coated diamond abrasive grains,the present modified/coated diamond abrasive grains may be firmlymounted on the substrate by thinner electroplated metal matrix. Thepresent modified diamond abrasive grains can be exposed from the fullcoverage and thinner electroplated metal matrix in large area so thatthe sawing rate/ability and polishing rate/free-cutting ability areimproved.

2. The thinner electroplated metal matrix can be applied for bonding thediamond abrasive grains on the substrate; therefore, the electroplatingprocess can benefit with less process time and cost. Moreover, themanufacturing efficiency of the electroplated tools, such aselectroplated polishing tools, electroplated sawing tools may beimproved.

3. Due to the micro-conductivity of the diamond abrasive grains, thediamond clusters/nodules may not happen on the substrate surface. Inother words, the diamond abrasive grains are separately and individuallydistributed on the surface of the substrate so that the surface accuracyof the electroplated tools is maintained.

4. Due to the micro-conductivity of the diamond abrasive grains, thequality of the electroplating layer on the diamond abrasive grains maybe improved.

The description above only illustrates specific embodiments and examplesof the present invention. The present invention should therefore covervarious modifications and variations made to the herein-describedstructure and operations of the present invention, provided they fallwithin the scope of the present invention as defined in the followingappended claims.

What is claimed is:
 1. A diamond abrasive grain, comprising: anelectrical conductive layer on the surface of the diamond abrasivegrain, the conductive layer having an outwardly increasing electricalconductibility along the thickness of the conductive layer, therebyproviding micro-conductivity of the diamond abrasive grain.
 2. Thediamond abrasive grain as claimed in claim 1, wherein the conductivelayer includes a metal content, and the metal content has a chemicalcomposition gradient along the direction of the thickness of theconductive layer.
 3. The diamond abrasive grain as claimed in claim 2,said metal content being at least one selected from the group consistingof boron, tungsten and transition metals, wherein the transition metalsis selected from the group consisting of titanium, chromium, vanadiumand zirconium, and the combination thereof.
 4. The diamond abrasivegrain as claimed in claim 1, wherein the conductive layer includes ametal-carbide content or a metal-nitride content, and the metal-carbidecontent or the metal-nitride content has an outwardly increasingchemical composition gradient along the thickness of the conductivelayer from the surface of the diamond abrasive grain.
 5. The diamondabrasive grain as claimed in claim 1, wherein the conductive layer hasan inner portion proximate the surface of the diamond abrasive grain,the inner portion has an electric resistance ranged from 70 to 100mΩ-cm, the conductive layer has an outer portion away from the surfaceof the diamond abrasive grain, the outer portion has an electricresistance ranged from 5 to 20 mΩ-cm.
 6. The diamond abrasive grain asclaimed in claim 1, wherein the diamond particle sized from 1 um to 600um.
 7. An electroplated abrasive tool, comprising: an abrasive surface;and a plurality of diamond abrasive grains firmly retained on theabrasive surface of the abrasive tool by an electroplated metal matrix,wherein each of the diamond abrasive grains includes a conductive layerwith electrical micro-conductibility on the surface of abrasive grains.8. The electroplated tool as claimed in claim 6, wherein the conductivelayer has a metal content therein and the metal content is a gradient ofchemical composition, said metal content comprises boron, tungsten ortransition metals, the transition metals comprises titanium, chromium,vanadium and zirconium.
 9. The electroplated tool as claimed in claim 6,wherein the conductive layer includes a metal-carbide content or ametal-nitride content therein, and the metal-carbide content or themetal-nitride content has an outwardly increasing chemical compositiongradient along the thickness of the conductive layer from the surface ofthe diamond abrasive grain.
 10. The electroplated tool as claimed inclaim 6, wherein the conductive layer has an inner portion proximate thesurface of the diamond abrasive grain, the inner portion has an electricresistance ranged from 70 to 100 mΩ-cm, the conductive layer has anouter portion away from the surface of the diamond abrasive grain, theouter portion has an electric resistance ranged from 5 to 20 mΩ-cm. 11.The electroplated tool as claimed in claim 6, wherein the electroplatedmetal matrix is partially or entirely plated on each of the diamondabrasive grains with particle size from 1 um to 600 um.